Energy effects in collisional neutralization with organic molecules

Abstract

Neutralization-reionization of CH3OH+., CH3NH2+. and (CH3)2NH+. ions was studied under conditions of exothermic and endothermic electron transfer and distributions of internal energy in the reionized ions were determined. The internal energy deposited on neutralization at kiloelectronvolt collision energies is governed by Franck-Condon effects for the systems under study, whereas the endothermic or exothermic energy balance in electron transfer from molecular targets has only a small effect on the high-energy fraction of the molecules formed. Electron transfer from low-lying molecular orbitals of the organic donor is suggested to occur during random orientations of the ion-molecule collision pair. The internal energy of the precursor ions to be neutralized has a large effect on the relative abundances of survivor ions in the spectra. Vertical recombination energies of CH3OH+. and CH3NH2+. are found by Gaussian-2 level calculations to differ substantially from vertical ionization energies of the corresponding neutral molecules. Franck-Condon effects are analyzed for the vibrational modes that are affected most by vertical electron transfer.